The present invention relates to a security system and a method of security service business, for example, relates to a system for inspecting for the presence or absence of a dangerous substance in a parcel, cargo, or a suspicious object in order to secure safeguard against dangerous substances. In this specification, “dangerous substance” means gunpowder which includes explosives, poisonous gases and inflammables.
At places where many people gather, such as airports and event sites, parcel inspections are generally conducted by using X-ray or metal detectors to ensure safety of passengers and event participants. When there is a possibility that an explosive or some other dangerous substances may be armed, an inspection must be performed to determine whether or not a dangerous substance exists, however, dangerous substance inspection devices are not commonly used yet. Currently, when there is a possibility that an explosive or some dangerous substances may be armed, it is common to summon professionals, who inspect for the presence or absence of a dangerous substance. This kind of dangerous substance inspection is required for inspecting parcels handled by door-to-door delivery services or inspecting a suspicious object in a bank's safety-deposit box.
The two most well-known and commonly used methods to detect dangerous substances are the gas chromatograph method and the mass spectrometric method. Both methods sample (sampling) any trace of gas emitting from a parcel or a suspicious object, analyze the sampled gas (sample gas), and inspect for the presence or absence of an element that is a part of a dangerous substance, such as an explosive.
The principle of the gas chromatograph method is as follows: A silica column having a treated inner surface, an iron column filled with adsorbent, or a glass column is heated and a sample gas is injected into it, and then, a carrier gas, such as nitrogen, helium or hydrogen, is injected into the column. This causes each element of the sample gas to separate and flow out from the column because of the difference of the boiling point or the difference of affinity between inner-surface treatment or filler material. This means that each element contained in the sample gas moves in the column at a different speed and therefore each element flows out from the column at a separate rate. The gas chromatograph method properly measures the degree of heat conductivity of the elements that separately flow out, confirms the mixing state of the sample and analyzes the elements.
RDX and TNT, the commonly used explosives, are usually identified by detecting NO2 which is an element of the explosives. However, NO2 is only one element in the explosive and it is difficult to confirm the structure of the compound based on the element. Therefore, reference data is obtained beforehand and relative comparison with the outflow time is conducted, and then it is determined whether or not a substance is an explosive, and in case of an explosive, the type of the explosive is identified. It takes several minutes to conduct a series of detecting processes. Also, a large amount of labor is required to maintain the device including the acquisition of the reference data for conducting relative comparison.
The mass spectrometric method ionizes a sample gas and measures the mass of the ion (accurately, the value m/z which has been obtained by dividing the ion mass m by electric charge z) by using a mass spectrometer placed in the vacuum. The mass spectrometer is classified into two types: a quadrupole mass spectrometer and an ion trap mass spectrometer.
The quadrupole mass spectrometer is a mass spectrometer which consists of four bar-shaped electrodes, wherein an electric field is formed at each electrode by the application of the direct current voltage and the high frequency voltage being superimposed. The ionized molecules of a sample gas are introduced to the electric field. Ions that pass through the electric field vibrate in three-dimensionally complicated behaviors, and only those ions that have a m/z ratio corresponding to the applied direct current voltage and high-frequency voltage are able to pass through the electric field and be detected. Other ions collide with one of the electrodes and become extinct. As a result, it is possible to obtain a spectrum by keeping the ratio of the direct current voltage and the high-frequency voltage constant and scanning the ions.
The ion trap mass spectrometer consists of two end cap electrodes and one ring electrode. When ionized molecules of a sample gas are introduced into an area within these three electrodes, the ions are enclosed (i.e. trapped) in the electric field which has been formed by the high frequency voltage applied to the ring electrode. The trapped ions are released according to their mass as a result of being scanned by another high frequency voltage which has been applied to the end cap electrodes. Accordingly, it is possible to obtain a spectrum by detecting the released ions. Ions are stored in the electric field and released after a certain time duration (e.g. dozens of msec order). This integrated effect makes it possible to attain supersensitivity.
By analyzing the mass spectrum data of a sample gas obtained in the manner mentioned above, it is possible to inspect for the presence or absence of a mass spectrum which is characteristic of a dangerous substance, such as explosives, which might be present in the sample gas. Consequently, it is possible to determine the presence or absence of a dangerous substance, such as explosives, and if such a substance exists, the type of the substance can be identified. This method requires only several seconds to detect an explosive (e.g. 3 to 8 seconds). Especially, the mass spectrometric method is highly reliable and its reliability can be increased further by employing a multiplex analysis which repeatedly conducts mass spectrometric processes by separating only ions (parent ion) characteristic of explosives from an ion mixture, activating the parent ions, and then detecting fragment ions (daughter ion) coming from the parent ions.